Fujitsu siemens Amilo LI keeps getting recurring problem

Ive got a fujitsu amilo LI3745 tower. Had it a while. But since original hard drive failure after 3 years. I have in the past 12 months had to replace hard drive twice. Due to PC issues resulting in corrupted files.At first, Fujitsu offline registation form comes up. Screen brighness fluctuates from dark to light.From there it goes from software not working. It wont allow system restore. Eventually coming completely unusable. Initially thought it was malware or virus attack. But nothing gets picked up.First time it did it. Took to PC repair place. He managed to get system restore to restore to factory settings. Checked for Malware but nothing showed up. However, 4-8 weeks down the line.Same thing took place! Thinking the replacement hard drive must be faulty. I went and got exact replacement as original. Reinstalled every thing. Everything worked ok for... 6-8 weeks; Thenthings started playing up again. If malware or virus must be an unknown one as no antivirus is picking it up. Norton (subscriber installed) or the one the repair guy used and suggested MALWARE free ware.Changed all my passwords once latest hard drive was installed. But looks like its back again?Very puzzling???

From your explanation I doubt this is a virus. More likely that something is corrupting the data on the hard disk. It is unusual to have two hard disk failures in such a short time and I'm unsure what evidence you had for the HD being the culprit again (assuming it was in the first place).

My guess is it is hardware or it's connections, most likely RAM. Download a RAM test and see if it finds anything.

I'm with Derek, another culprit could be your power supply ( PSU )http://is.gd/g5W6A9Dust is one of your big enemies, leads to overheating & component failure.Make sure the PSU fan & all the others are spinning fast.

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